Relative Influence of Host, Wolbachia, Geography and Climate on the Genetic Structure of the Sub-saharan Parasitic Wasp Cotesia sesamiae

Abstract

The parasitoid lifestyle represents one of the most diversified life history strategies on earth. There are however very few studies on the variables associated with intraspecific diversity of parasitoid insects, especially regarding the relationship with spatial, biotic and abiotic ecological factors. Cotesia sesamiae is a Sub-Saharan stenophagous parasitic wasp that parasitizes several African stemborer species with variable developmental success. The different host-specialized populations are infected with different strains of Wolbachia, an endosymbiotic bacterium widespread in arthropods that is known for impacting life history traits, notably reproduction, and consequently species distribution. In this study, first we analyzed the genetic structure of C. sesamiae across Sub-Saharan Africa, using 8 microsatellite markers. We identified five major population clusters across Sub-Saharan Africa, which probably originated in the East African Rift region and expanded throughout Africa in relation to host genus and abiotic factors, such as Köppen-Geiger climate classification. Using laboratory lines, we estimated the incompatibility between the different strains of Wolbachia infecting C. sesamiae. We observed that incompatibility between Wolbachia strains was asymmetric, expressed in one direction only. Based on these results, we assessed the relationships between the direction of gene flow and Wolbachia infections in the genetic clusters. We found that host specialization was more influential on genetic structure than Wolbachia-induced reproductive incompatibility, which in turn was more influential than geography and current climatic conditions. These results are discussed in the context of African biogeography, and co-evolution between Wolbachia, virus parasitoid and host, in the perspective of improving biological control efficiency through a better knowledge of biological control agents' evolutionary ecology.

Managing and monitoring genetic isolation and local adaptation of endemic and introduced Cotesia sesamiae for the biological control of the cereal stemborer Busseola fusca in Cameroon

“…In hybridization experiments, the number of females in the offspring is reduced in both directions of mating. Incompatibility is total for ♀east x ♂west and weak for ♀west x ♂east (Branca et al 2019). Branca et al ( 2019supplementary data) estimated an infection rate of 92% across Africa, which somewhat reduces incompatibility.…”

“…In Cameroon, endemic C. sesamiae in wild habitats are infected by the A or A+Beast Wolbachia strains (Branca et al 2009). Interestingly the incompatibility of the Cameroonian strains is stronger than that of the Kenyan strains (Branca et al, 2019); therefore, differences in Wolbachia strains could be used to protect endemic Cameroonian populations from hybridization with introduced Kenyan strains.…”

“…The aim was to produce Kenyan strains for release that were either not infected or infected by a Bwest Wolbachia strain, not present in Cameroon (Branca et al 2019). The variant of Wolbachia present in each strain was identified with the wsp gene AFLP test (Branca et al 2011) using two individuals per population, before and after mass production in the laboratory.…”

“…Incompatibilities can be unidirectional (when infected males mate with a non-infected females) or bidirectional (through matings between insects harboring different strains of the bacterium). Four Wolbachia variants have been identified from C. sesamiae collected in Kenya on maize (Mochiah et al 2002;Gounou et al, 2008;Branca et al 2019). In western Kenya, the parasitoid developing on B. fusca is infected by the Bwest variant, while in the eastern coastal region the parasitoid developing on the noctuid cereal stemborer Sesamia calamistis Hampson, it is infected by the A, Beast and the co-infection…”

Biopesticide Research and Product Development in Africa for Sustainable Agriculture and Food Security – Experiences From the International Centre of Insect Physiology and Ecology (icipe)

“…Wolbachia sp. also plays a critical role in determining the genetic structure of C. sesamiae in sub-Saharan Africa (Branca et al, 2019) and can influence the diversity of the host. Close association of species-specific gut microbiomes can be useful to differentiate between sibling species as reported with Ceratitis rosa s. s and C. quilici (Khamis et al, 2020).…”